Validating my page

Ok no template validates on bobbys site not eben the default theme.
On tidy mine has a real problem in the way it looks. I have no idea why though. I do not understand what I am going to learn from this. I already know there is a problem. I can’t find it. I am not a programmer I am a blogger. But no one makes a theme I like. So I am forced to change it. What should I do now?